TPS79401, TPS79418 TPS79425, TPS79428 TPS79430, TPS79433 www.ti.com SLVS349D – NOVEMBER 2001 – REVISED OCTOBER 2004 ULTRALOW-NOISE, HIGH PSRR, FAST RF 250-mA LOW-DROPOUT LINEAR REGULATORS FEATURES • • • • • • • 250-mA Low-Dropout Regulator With Enable Available in 1.8 V, 2.5 V, 2.8 V, 3 V, 3.3 V, and Adjustable (1.2 V to 5.5 V) High PSRR (60 dB at 10 kHz) Ultralow Noise (32 µVrms, TPS79428) Fast Start-Up Time (50 µs) Stable With a 2.2-µF Ceramic Capacitor Excellent Load/Line Transient Response Very Low Dropout Voltage (155 mV at Full Load) Available in MSOP-8 and SOT223-6 Packages The TPS794xx family of low-dropout (LDO) linear voltage regulators features high power-supply rejection ratio (PSRR), ultralow-noise, fast start-up, and excellent line and load transient responses in small outline, MSOP-8 PowerPAD™ and SOT223-6 packages. Each device in the family is stable with a small 2.2-µF ceramic capacitor on the output. The family uses an advanced, proprietary BiCMOS fabrication process to yield extremely low dropout voltages (e.g., 155 mV at 250 mA). Each device achieves fast start-up times (approximately 50 µs with a 0.001-µF bypass capacitor) while consuming low quiescent current (170 µA typical). Moreover, when the device is placed in standby mode, the supply current is reduced to less than 1 µA. The TPS79428 exhibits approximately 32 µVRMS of output voltage noise at 2.8 V output with a 0.1-µF bypass capacitor. Applications with analog components that are noise-sensitive, such as portable RF electronics, benefit from the high PSRR and low noise features as well as the fast response time. APPLICATIONS • • • • • RF: VCOs, Receivers, ADCs Audio Bluetooth™, Wireless LAN Cellular and Cordless Telephones Handheld Organizers, PDAs DGN PACKAGE MSOP PowerPAD (TOP VIEW) 1 2 3 4 8 7 6 5 IN NC EN GND NC − No internal connection DCQ PACKAGE SOT223-6 (TOP VIEW) EN IN GND OUT NR 1 2 3 4 5 0.35 80 IOUT = 10 mA 70 IOUT = 250 mA 60 50 40 30 VIN = 4.3 V, VOUT = 3.3 V, CIN = 1 µF, COUT = 10 µF, CNR = 0.01 µF 20 6 GND TPS79428 OUTPUT SPECTRAL NOISE DENSITY vs FREQUENCY 90 Ripple Rejection (dB) OUT NC FB NR TPS79433 RIPPLE REJECTION vs FREQUENCY Output Spectral Noise Density (µV/√Hz) • • DESCRIPTION 10 0 10 100 1k COUT = 2.2 µF, CNR = 0.1 µF, VIN = 3.8 V 0.30 0.25 IOUT = 250 mA 0.20 0.15 0.10 IOUT = 1 mA 0.05 0 10 k 100 k Frequency (Hz) 1M 10 M 100 1000 10000 100000 Frequency (Hz) Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. Bluetooth is a trademark of Bluetooth SIG, Inc. PowerPAD is a trademark of Texas Instruments. All other trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2001–2004, Texas Instruments Incorporated TPS79401, TPS79418 TPS79425, TPS79428 TPS79430, TPS79433 www.ti.com SLVS349D – NOVEMBER 2001 – REVISED OCTOBER 2004 This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. ORDERING INFORMATION PRODUCT TPS79401 VOLTAGE PACKAGE TJ MSOP-8 AXL SOT223-6 PS79401 Adjustable MSOP-8 TPS79418 TPS79423 SYMBOL AXM 1.8 V SOT223-6 PS79418 MSOP-8 AYB 2.5 V SOT223-6 PS79425 -40°C to 125°C MSOP-8 TPS79428 2.8 V SOT223-6 TPS79430 TPS79433 2 AYC PS79428 MSOP-8 AYD SOT223-6 PS79430 3V MSOP-8 AYE SOT223-6 PS79433 3.3 V PART NUMBER TRANSPORT MEDIA, QUANTITY TPS79401DGNR Tape and Reel, 2500 TPS79401DGNT Tape and Reel, 250 TPS79401DCQR Tape and Reel, 2500 TPS79401DCQ Tube, 78 TPS79418DGNR Tape and Reel, 2500 TPS79418DGNT Tape and Reel, 250 TPS79418DCQR Tape and Reel, 2500 TPS79418DCQ Tube, 78 TPS79425DGNR Tape and Reel, 2500 TPS79425DGNT Tape and Reel, 250 TPS79425DCQR Tape and Reel, 2500 TPS79425DCQ Tube, 78 TPS79428DGNR Tape and Reel, 2500 TPS79428DGNT Tape and Reel, 250 TPS79428DCQR Tape and Reel, 2500 TPS79428DCQ Tube, 78 TPS79430DGNR Tape and Reel, 2500 TPS79430DGNT Tape and Reel, 250 TPS79430DCQR Tape and Reel, 2500 TPS79430DCQ Tube, 78 TPS79433DGNR Tape and Reel, 2500 TPS79433DGNT Tape and Reel, 250 TPS79433DCQR Tape and Reel, 2500 TPS79433DCQ Tube, 78 TPS79401, TPS79418 TPS79425, TPS79428 TPS79430, TPS79433 www.ti.com SLVS349D – NOVEMBER 2001 – REVISED OCTOBER 2004 ABSOLUTE MAXIMUM RATINGS over operating temperature range unless otherwise noted (1) VALUE VIN range -0.3 V to 6 V VEN range -0.3 V to VIN + 0.3 V VOUT range -0.3 V to 6 V Peak output current Internally limited ESD rating, HBM 2 kV ESD rating, CDM 500 V Continuous total power dissipation See Dissipation Ratings Table Junction temperature range, TJ -40°C to 150°C Storage temperature range, Tstg -65°C to 150°C (1) Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under recommended operating conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. PACKAGE DISSIPATION RATINGS PACKAGE AIR FLOW (CFM) RθJC(°C/W) RθJA(°C/W) TA ≤ 25°C POWER RATING TA = 70°C POWER RATING TA = 85°C POWER RATING 0 8.47 55.09 2.27 W 1.45 W 1.18 W DGN 150 8.21 49.97 2.50 W 1.60 W 1.30 W 250 8.20 48.10 2.60 W 1.66 W 1.35 W 6 5 PD (W) 4 Condition 1 CONDITIONS 3 1 2 Condition 2 2 PACKAGE SOT223 SOT223 PCB AREA 4in2 Top Side Only 0.5in2 Top Side Only θJA 53°C/W 110°C/W 1 0 0 25 50 75 100 TA (°C) 125 150 Figure 1. SOT223 Power Dissipation 3 TPS79401, TPS79418 TPS79425, TPS79428 TPS79430, TPS79433 www.ti.com SLVS349D – NOVEMBER 2001 – REVISED OCTOBER 2004 ELECTRICAL CHARACTERISTICS Over recommended operating temperature range (TJ = -40°C to 125°C), VEN = VIN, VIN = VOUT(nom) + 1 V (1), IOUT = 1mA, COUT = 10µF, CNR = 0.01 µF, unless otherwise noted. Typical values are at 25°C. PARAMETER VIN Input voltage (1) IOUT Continuous output current VFB Internal reference VOUT Output voltage range TEST CONDITIONS MIN 0 TPS79401 TJ = 25°C 1.220 TPS79401 Accuracy (1) VOUT + 1 V ≤ VIN ≤ 5.5 V Output voltage line regulation (∆VOUT%/∆VIN) (1) VOUT + 1 V < VIN ≤ 5.5 V Load regulation (∆VOUT%/∆IOUT) 0 µA < IOUT < 250 mA 0 mA ≤ IOUT ≤ 250 mA UNIT 5.5 V 250 mA 1.230 V VFB 5.5 - VDO V -3.0 +3.0 % 0.12 %/V 0.05 10 mV IOUT = 250 mA 155 210 TPS79430 IOUT = 250 mA 155 210 TPS79433 IOUT = 250 mA 145 200 Output current limit VOUT = 0 V 925 Ground pin current 0 µA < IOUT < 250 mA 170 220 µA Shutdown current (3) VEN = 0 V 0.07 1 µA FB pin current VFB = 1.8 V 1 µA Power-supply ripple rejection TPS79428 Output noise voltage (TPS79428) Time, start-up (TPS79428) 2.7 V < VIN < 5.5 V f = 100 Hz IOUT = 250 mA 65 f = 10 kHz IOUT = 250 mA 60 f = 100 kHz IOUT = 250 mA 40 CNR = 0.001 µF 55 CNR = 0.0047 µF 36 CNR = 0.01 µF 33 CNR = 0.1 µF 32 CNR = 0.001 µF 50 BW = 100 Hz to 100 kHz, IOUT = 250 mA RL - 14 Ω, COUT = 1 µF CNR = 0.0047 µF mV mA dB µVRMS 70 CNR = 0.01 µF µs 100 High-level enable input voltage 2.7 V < VIN < 5.5 V 1.7 VIN Low-level enable input voltage 2.7 V < VIN < 5.5 V 0 0.7 V EN pin current VEN = 0 1 1 µA UVLO threshold VCC rising UVLO hysteresis 4 1.225 MAX TPS79428 Dropout voltage (2) VIN = VOUT(nom) - 0.1 V (1) (2) (3) TYP 2.7 Minimum VIN is 2.7 V or VOUT + VDO, whichever is greater. Dropout is not measured for the TPS79418 and TPS79425 since minimum VIN = 2.7 V. For adjustable versions, this applies only after VIN is applied; then VEN transitions high to low. 2.25 2.65 100 V V mV TPS79401, TPS79418 TPS79425, TPS79428 TPS79430, TPS79433 www.ti.com SLVS349D – NOVEMBER 2001 – REVISED OCTOBER 2004 FUNCTIONAL BLOCK DIAGRAM—ADJUSTABLE VERSION OUT IN Current Sense UVLO SHUTDOWN ILIM R1 _ GND + FB EN UVLO R2 Thermal Shutdown Quickstart Bandgap Reference 1.225 V VIN 250 kΩ External to the Device Vref NR(1) (1) Not Available on DCQ (SOT223) options. FUNCTIONAL BLOCK DIAGRAM—FIXED VERSION OUT IN UVLO Current Sense GND SHUTDOWN ILIM R1 _ EN + UVLO Thermal Shutdown R2 Quickstart VIN R2 = 40k Bandgap Reference 1.225 V 250 kΩ Vref NR Terminal Functions TERMINAL DESCRIPTION NAME DGN (MSOP) DCQ (SOT223) NR 4 5 Connecting an external capacitor to this pin bypasses noise generated by the internal bandgap. This improves power-supply rejection and reduces output noise. EN 6 1 The EN terminal is an input which enables or shuts down the device. When EN goes to a logic high, the device will be enabled. When the device goes to a logic low, the device is in shutdown mode. FB 3 5 This terminal is the feedback input voltage for the adjustable device. GND 5, PAD 3 Regulator ground. IN 8 2 Unregulated input to the device. NC 2, 7 OUT 1 No internal connection. 4 Output of the regulator. 5 TPS79401, TPS79418 TPS79425, TPS79428 TPS79430, TPS79433 www.ti.com SLVS349D – NOVEMBER 2001 – REVISED OCTOBER 2004 TYPICAL CHARACTERISTICS TPS79433 OUTPUT VOLTAGE vs OUTPUT CURRENT TPS79428 OUTPUT VOLTAGE vs JUNCTION TEMPERATURE 3.290 TPS79428 GROUND CURRENT vs JUNCTION TEMPERATURE 190 2.800 3.285 IOUT = 1 mA 2.795 VIN = 3.8 V, COUT = 10 µF 185 3.280 180 IOUT = 1 mA 3.270 3.265 3.255 2.780 2.765 0 50 100 IOUT (mA) 200 250 170 IOUT = 250 mA 160 IOUT = 200 mA −40 −25 −10 5 155 150 −40 −25 −10 5 20 35 50 65 80 95 110 125 TJ (°C) 20 35 50 65 80 95 110 125 TJ (°C) Figure 2. Figure 3. Figure 4. TPS79428 OUTPUT SPECTRAL NOISE DENSITY vs FREQUENCY TPS79428 OUTPUT SPECTRAL NOISE DENSITY vs FREQUENCY TPS79428 OUTPUT SPECTRAL NOISE DENSITY vs FREQUENCY Output Spectral Noise Density (µV/√Hz) 0.30 0.25 0.20 IOUT = 250 mA 0.15 0.10 IOUT = 1 mA 0.05 1.8 0.35 COUT = 2.2 µF, CNR = 0.1 µF, VIN = 3.8 V COUT = 10 µF, CNR = 0.1 µF, VIN = 3.8 V 0.30 Output Spectral Noise Density (µV/√Hz) 0.35 0.25 0.20 IOUT = 1 mA 0.15 0.10 IOUT = 250 mA 0.05 100 1000 10000 100 100000 1000 10000 COUT = 10 µF, IOUT = 250 mA VIN = 3.8 V 1.6 1.4 CNR = 0.001 µF 1.2 CNR = 0.0047 µF 1.0 CNR = 0.01 µF 0.8 CNR = 0.1 µF 0.6 0.4 0.2 0 100 0 0 100000 1000 10000 100000 Frequency (Hz) Frequency (Hz) Frequency (Hz) Figure 5. Figure 6. Figure 7. TPS79428 ROOT MEAN SQUARED OUTPUT NOISE vs CNR TPS79433 OUTPUT IMPEDANCE vs FREQUENCY TPS79428 DROPOUT VOLTAGE vs JUNCTION TEMPERATURE 10 60 VIN = 3.8 V, COUT = 10 µF 40 30 20 200 IOUT = 250 mA IOUT = 1 mA 1 VDO (mV) ZO, Output Impedance (Ω) 50 250 VIN = 4.3 V, COUT = 10 µF, IOUT = 250 mA, COUT = 10 µF 0 0.001 Figure 8. 0.1 100 50 IOUT = 1 mA 0.020 0.0047 0.01 CNR (µF) 150 IOUT = 250 mA 0.100 10 6 175 165 2.770 3.250 Output Spectral Noise Density (µV/√Hz) 2.785 2.775 3.260 RMS Output Noise (µVRMS) VIN = 3.8 V COUT = 10 µF IGND (µA) 3.275 V OUT (V) V OUT (V) 2.790 10 100 1k 10 k 100 k Frequency (Hz) Figure 9. 1M 10 M 0 −40 −25 −10 5 20 35 50 65 80 95 110 125 TJ (°C) Figure 10. TPS79401, TPS79418 TPS79425, TPS79428 TPS79430, TPS79433 www.ti.com SLVS349D – NOVEMBER 2001 – REVISED OCTOBER 2004 TYPICAL CHARACTERISTICS (continued) TPS79433 RIPPLE REJECTION vs FREQUENCY 90 90 80 80 IOUT = 250 mA 60 50 40 VIN = 4.3 V, VOUT = 3.3 V, CIN = 1 µF, COUT = 10 µF, CNR = 0.01 µF 10 0 10 100 70 60 50 40 VIN = 4.3 V, VOUT = 3.3 V, CIN = 1 µF, COUT = 2.2 µF, CNR = 0.01 µF 20 10 1k 10 k 100 k 1M 10 10 M 30 VIN = 4.3 V, VOUT = 3.3 V, CIN = 1 µF, COUT = 2.2 µF, CNR = 0.1 µF 10 10 k 100 k 1M 0 10 M 10 100 1k 10 k 100 k 1M 10 M Figure 11. Figure 12. Figure 13. TPS79433 OUTPUT VOLTAGE, ENABLE VOLTAGE vs TIME (START-UP) TPS79433 LINE TRANSIENT RESPONSE TPS79433 LOAD TRANSIENT RESPONSE VIN (V) VIN = 4.3 V, VOUT = 3.3 V, IOUT = 250 mA, COUT = 2.2 µF Frequency (Hz) IOUT = 250 mA,COUT = 10 µF, CNR = 0.1 µF, dv/dt = 1 V/µs 5.5 5.0 250 50 0 4.5 10 3 ∆VOUT (mV) VOUT, VEN (V) 40 Frequency (Hz) 6.0 CNR = 0.0047 µF 2 CNR = 0.001 µF 1 0 −10 0 −50 −20 0 0 80 160 240 320 400 480 560 640 720 800 100 200 300 400 0 500 30 60 90 120 0.02A s 150 180 210 Time (µs) Time (µs) Figure 14. Figure 15. Figure 16. TPS79425 POWER-UP/POWER-DOWN TPS79433 DROPOUT VOLTAGE vs OUTPUT CURRENT TPS79401 DROPOUT VOLTAGE vs INPUT VOLTAGE Time (µs) 4.5 250 200 VOUT = 2.5 V, RL = 10 Ω 4.0 di dt VIN = 4.3 V, COUT = 10 µF −30 0 TA = 125°C TA = 125°C TA = 25°C 200 3.5 150 VIN 3.0 VOUT 2.0 1.5 VDO (mV) TA = 25°C 2.5 VDO (mV) Power-Up (500 mV/div) 1k 50 Frequency (Hz) V_Enable 0 100 IOUT = 250 mA 60 20 0 4 2 70 IOUT = 250 mA 30 IOUT = 10 mA 80 IOUT = 10 mA IOUT (mA) 20 90 ∆VOUT (mV) 30 TPS79433 RIPPLE REJECTION vs FREQUENCY Ripple Rejection (dB) Ripple Rejection (dB) IOUT = 10 mA 70 Ripple Rejection (dB) TPS79433 RIPPLE REJECTION vs FREQUENCY 100 150 100 TA = −40°C TA = −40°C 1.0 50 COUT = 10 µF, CNR = 0.01 µF, IOUT = 250 mA 50 0.5 0 −0.5 0 0 1.4 2.8 4.2 5.6 t (ms) Figure 17. 7.0 8.4 9.8 0 25 50 75 100 125 150 175 200 225 250 IOUT (mA) Figure 18. 0 2.5 3.0 3.5 4.0 4.5 5.0 VIN (V) Figure 19. 7 TPS79401, TPS79418 TPS79425, TPS79428 TPS79430, TPS79433 www.ti.com SLVS349D – NOVEMBER 2001 – REVISED OCTOBER 2004 TYPICAL CHARACTERISTICS (continued) TPS79428 TYPICAL REGIONS OF STABILITY EQUIVALENT SERIES RESISTANCE (ESR) vs OUTPUT CURRENT COUT = 2.2 µF TA = −40 to 85°C 10 Region of Instability 1 0.1 Region of Stability 0.01 COUT = 10 µF TA = −40 to 85°C 10 Region of Instability 1 0.1 Region of Stability 0.01 0 25 50 75 100 125 150 175 200 225 250 IOUT (mA) Figure 20. 8 100 ESR, Equivalent Series Resistance (Ω) ESR, Equivalent Series Resistance (Ω) 100 TPS79428 TYPICAL REGIONS OF STABILITY EQUIVALENT SERIES RESISTANCE (ESR) vs OUTPUT CURRENT 1 10 20 40 60 80 IOUT (mA) Figure 21. 120 200 250 TPS79401, TPS79418 TPS79425, TPS79428 TPS79430, TPS79433 www.ti.com SLVS349D – NOVEMBER 2001 – REVISED OCTOBER 2004 APPLICATION INFORMATION The TPS794xx family of low-dropout (LDO) regulators has been optimized for use in noise-sensitive equipment. The device features extremely low dropout voltages, high PSRR, ultralow output noise, low quiescent current, and enable input to reduce supply currents to less than 1 µA when the regulator is turned off. A typical application circuit is shown in Figure 22. VIN IN VOUT OUT TPS794xx EN GND NR 0.1µF 2.2µF 0.01µF Figure 22. Typical Application Circuit External Capacitor Requirements A 0.1-µF or larger ceramic input bypass capacitor, connected between IN and GND and located close to the TPS794xx, is required for stability. It improves transient response, noise rejection, and ripple rejection. A higher-value input capacitor may be necessary if large, fast-rise-time load transients are anticipated or the device is located several inches from the power source. Like most low dropout regulators, the TPS794xx requires an output capacitor connected between OUT and GND to stabilize the internal control loop. The minimum recommended capacitance is 2.2 µF. Any 2.2 µF or larger ceramic capacitor is suitable. The internal voltage reference is a key source of noise in an LDO regulator. The TPS794xx has an NR pin which is connected to the voltage reference through a 250-kΩ internal resistor. The 250-kΩ internal resistor, in conjunction with an external bypass capacitor connected to the NR pin, creates a low-pass filter to reduce the voltage reference noise and, therefore, the noise at the regulator output. In order for the regulator to operate properly, the current flow out of the NR pin must be at a minimum, because any leakage current creates an IR drop across the internal resistor thus creating an output error. Therefore, the NR capacitor must have minimal leakage current. The bypass capacitor should be no more than 0.1 µF to ensure that it is fully charged during the quickstart time provided by the internal switch shown in the functional block diagram. For example, the TPS79428 exhibits only 32 µVRMS of output voltage noise using a 0.1-µF ceramic NR capacitor and a 2.2-µF ceramic output capacitor. Note that the output starts up slower as the bypass capacitance increases due to the RC time constant at the NR pin that is created by the internal 250-kΩ resistor and external capacitor. 9 TPS79401, TPS79418 TPS79425, TPS79428 TPS79430, TPS79433 www.ti.com SLVS349D – NOVEMBER 2001 – REVISED OCTOBER 2004 Board Layout Recommendation to Improve PSRR and Noise Performance To improve ac measurements like PSRR, output noise, and transient response, it is recommended that the board be designed with separate ground planes for VIN and VOUT, with each ground plane connected only at the ground pin of the device. In addition, the ground connection for the bypass capacitor should connect directly to the ground pin of the device. THERMAL RESISTANCE vs PCB COPPER AREA Thermal Resistance − θ JA ( ° C/W ) 180 CIRCUIT BOARD COPPER AREA Surface-Mount Package 1 oz. Copper 160 140 120 100 80 60 40 20 SOT223 Surface-Mount Package 0 0 1 2 3 4 5 PCB Copper Area − in Figure 23. Thermal Resistance vs PCB Area for the SOT223-6. Power and Dissipation and Junction Temperature Specified regulator operation is assured to a junction temperature of 125°C; the maximum junction temperature should be restricted to 125°C under normal operating conditions. This restriction limits the power dissipation the regulator can handle in any given application. To ensure the junction temperature is within acceptable limits, calculate the maximum allowable dissipation, PD(max), and the actual dissipation, PD, which must be less than or equal to PD(max). The maximum-power-dissipation limit is determined using the following equation: T max T A P J D(max) R θJA (1) where: • TJmax is the maximum allowable junction temperature. • RθJA is the thermal resistence juntion-to-ambient for the package. See the power dissipation table and Figure 1 • TA is the ambient temperature. The regulator dissipation is calculated using: P D V IN V OUT IOUT (2) Power dissipation resulting from quiescent current is negligible. Excessive power dissipation triggers the thermal protection circuit. Regulator Mounting The tab of the SOT223-6 package is electrically connected to ground. For best thermal performance, the tab of the surface-mount version should be soldered directly to a circuit-board copper area. Increasing the copper area improves heat dissipation. Solder pad footprint recommendations for the devices are presented in an application bulletin Solder Pad Recommendations for Surface-Mount Devices, literature number AB-132, available from the TI web site (www.ti.com). 10 TPS79401, TPS79418 TPS79425, TPS79428 TPS79430, TPS79433 www.ti.com SLVS349D – NOVEMBER 2001 – REVISED OCTOBER 2004 Programming the TPS79401 Adjustable LDO Regulator The output voltage of the TPS79401 adjustable regulator is programmed using an external resistor divider as shown in Figure 24. The output voltage is calculated using: V OUT V REF 1 R1 R2 (3) where: • VREF = 1.2246 V typ (the internal reference voltage). Resistors R1 and R2 should be chosen for approximately 40-µA divider current. Lower value resistors can be used for improved noise performance, but the device wastes more power. Higher values should be avoided as leakage current at FB increases the output voltage error. The recommended design procedure is to choose R2 = 30.1 kΩ to set the divider current at 40 µA, C1 = 15 pF for stability, and then calculate R1 using: V R1 OUT 1 V REF R2 (4) In order to improve the stability of the adjustable version, it is suggested that a small compensation capacitor be placed between OUT and FB. For voltages < 1.8 V, the value of this capacitor should be 100 pF. For voltages > 1.8 V, the approximate value of this capacitor can be calculated as: (3 x 10 –7) x (R1 R2) C1 (R1 x R2) (5) The suggested value of this capacitor for several resistor ratios is shown in the table below. If this capacitor is not used (such as in a unity-gain configuration) or if an output voltage < 1.8 V is chosen, then the minimum recommended output capacitor is 4.7 µF instead of 2.2 µF. OUTPUT VOLTAGE PROGRAMMING GUIDE VIN IN 1 µF R1 EN NR GND FB 0.01 µF † VOUT OUT TPS794xx R2 C1 2.2 µF OUTPUT VOLTAGE R1 R2 C1 2.5 V 31.6 kΩ 30.1 kΩ 22 pF 3.3 V 49.9 kΩ 30.1 kΩ 15 pF 3.6 V 59 kΩ 30.1 kΩ 15 pF Not Available on the DCQ package. Figure 24. TPS79401 Adjustable LDO Regulator Programming Regulator Protection The TPS794xx PMOS-pass transistor has a built-in back diode that conducts reverse current when the input voltage drops below the output voltage (e.g., during power-down). Current is conducted from the output to the input and is not internally limited. If extended reverse voltage operation is anticipated, external limiting might be appropriate. The TPS794xx features internal current limiting and thermal protection. During normal operation, the TPS794xx limits output current to approximately 925 mA. When current limiting engages, the output voltage scales back linearly until the overcurrent condition ends. While current limiting is designed to prevent gross device failure, care should be taken not to exceed the power dissipation ratings of the package or the absolute maximum voltage rating of the device. If the temperature of the device exceeds approximately 165°C, thermal-protection circuitry shuts it down. Once the device has cooled down to below approximately 140°C, regulator operation resumes. 11 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. 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